The paper researched the variation of discharge water temperature in the process with time and the completion of reservoirs according to the measured data of discharge water temperature in Wujiangdu reservoir. Also the paper analyzed the cumulative effects of low-temperature discharge in the upstream on the discharge water temperature of the downstream with the EFDC model.The results showed that vertical distribution of water temperature hierarchy was more obvious with lower discharge water temperature of the upstream reservoir, meanwhile the cumulative effect was larger.